The present invention relates to chuck assemblies of the general types which are adapted to be mounted on the spindle of a machine tool for accurately holding a workpiece during a machining operation. Problems are frequently encountered with chuck assemblies of the types designed to chuck elongated workpieces such as poppet-type engine valves, water pump shafts and replaceable piercetype punches and the like in which the workpiece extends a substantial distance forwardly of the work engaging jaws to provide sufficient access for the cutting tool to act on the surface of the workpiece to be machined. The projection of the workpiece in unsupported relationship beyond the work engaging jaws serves to amplify any misalignment present between the axis of the workpiece and the longitudinal axes of the chuck and machine tool assembly which detracts from achieving the precise dimensional accuracy required in many instances.
The resiliency of the unsupported portion of the workpiece projecting forwardly of the work engaging jaws has also occasioned some difficulty in achieving the desired machining accuracy and/or surface finish. The seriousness of this problem is dependent, to some extent, on the type of machining operation being performed, the type of workpiece being machined and the distance at which the machining operation takes place from the forward portion of the work engaging jaws.
Some of the foregoing problems have been overcome by employing work holding chucks of the double-diaphragm type such as shown in U.S. Pat. No. 2,565,430, which is assigned to the same assignee of the present invention. The cost of such double-diaphragm type chucks and the high degree of care and skill required to effect an accurate adjustment has somewhat detracted from a more widespread use thereof. The difficulty of maintaining such chucks in precise adjustment has been further aggravated by a gradual wear during use of the work engaging jaws and the periodic change in the types of workpieces being processed, requiring a change in the chuck assembly or a major modification in the adjustment of the engaging jaws in order to accommodate such different workpieces.
The chuck assembly of the present invention overcomes the problems and disadvantages associated with prior art work holders in providing a chuck which is of durable operation, simple construction, versatile use, easy to adjust and maintain in accurate alignment, and of economical cost.